I often hear people unscientifically stating that men generally generally die younger because of the higher stress encountered in their work lives. I would personally immediately rule this out, as who's to say that that women's (past) home lives just weren't as stressful? Also, shouldn't we see a narrowing of difference in age with the recent gender equality issues? Since the trend in question still occurs in virtually all countries of the world, I think it's safe to assume that the phenomenon is purely physiological.

I am curious as to the most sound scientific theories or known reasons for why women typically outlive men. Finally, I understand that aging in itself is not a process that's completely understood, and thus am not expecting a "complete list" of factors.

3 Answers
3

In a study on longevity in 121 countries, women tended to outlive men by about 5 years [1]. The suggested causes for this are numerous, some of which are temporally, geographically, or culturally specific.

On the terminology, sex tends to refer to the absolute biological differences, whereas gender relates more to differences in perception/lifestyle (for instance, socio-economic differences).

Evidence

In a study on Greek centenarians the authors found that women outnumbered men (1.68:1), with men having a higher likelihood of smoking, and thus are more at risk of smoking-related illness and mortality (historically this was more true than today) [2]. This is also true for alcohol consumption. The authors also report that having a first degree relative who was also a centenarian is associated with longevity (highlighting the importance of genetic factors in lifespan determination).

There is also evidence that the rate of telomere shortening (number of cell-divisions until cell-cycle arrest) is sex-specific [3].

rwst cites an interesting paper, that presents evidence that suggests male hormones may decrease lifespan [4]. This may be due to differential onset of atherosclerosis and cardiovascular disease, caused by exposure to different sex hormones [5].

In a review on the brain/behaviour specific aspects of differential ageing between the sexes, the authors discuss differences in brain anatomy and cognitive (and emotional) functionality between the sexes [6].

Remarks

This is by no means an exhaustive list of the reasons for differences in lifespan between the sexes in humans. There are likely to be many other causes, such as men tending to have more 'risky' behaviours, and possibly other unknown genetic effects, such as having 2 X chromosomes, vs. XY.

Update

Just been reading this interesting paper by Maklakov, et al (2013, BioEssays) titled "Evolution of sex differences in lifespan and aging: Causes and constraints", which presents a more evolutionary/genetic argument for the differences.

Abstract

Why do the two sexes have different lifespans and rates of aging? Two hypotheses based on asymmetric inheritance of sex chromosomes (“unguarded X”) or mitochondrial genomes (“mother's curse”) explain sex differences in lifespan as sex-specific maladaptation leading to increased mortality in the shorter-lived sex. While asymmetric inheritance hypotheses equate long life with high fitness, considerable empirical evidence suggests that sexes resolve the fundamental tradeoff between reproduction and survival differently resulting in sex-specific optima for lifespan. However, selection for sex-specific values in life-history traits is constrained by intersexual genetic correlations resulting in intra-locus sexual conflict over optimal lifespan. The available data suggest that the evolution of sexual dimorphism only partially resolves these conflicts. Sexual conflict over optimal trait values, which has been demonstrated in model organisms and in humans, is likely to play a key role in shaping the evolution of lifespan, as well as in maintaining genetic variation for sex-specific diseases.

Although many studies have shown that there are trade-offs between
longevity and reproduction, whether such trade-offs exist in humans
has been a matter of debate [1,2]. In many species, including humans,
males live shorter than females, which could be due to the action of
male sex hormones. Castration, which removes the source of male sex
hormones, prolongs male lifespan in many animals, but this issue has
been debated in humans [3]. To examine the effects of castration on
longevity, we analyzed the lifespan of historical Korean eunuchs.
Korean eunuchs preserved their lineage by adopting castrated boys. We
studied the genealogy records of Korean eunuchs and determined the
lifespan of 81 eunuchs. The average lifespan of eunuchs was 70.0 ±
1.76 years, which was 14.4–19.1 years longer than the lifespan of
non-castrated men of similar socio-economic status. Our study supports
the idea that male sex hormones decrease the lifespan of men.

$\begingroup$Are they really saying that the lifespan of their control samples (i.e. men with testes) was only 51-56 years? That is worryingly low - I suspect that something else may be going on there .. ?$\endgroup$
– PoshpawsSep 28 '12 at 8:30

$\begingroup$Ahh! That makes sense then :-) Even so, it would be interesting to know if they accounted for things like syphilis which might make sense in the context of this study. OK, I should read the paper ...$\endgroup$
– PoshpawsSep 28 '12 at 10:12

$\begingroup$I'd also add that differences in the lifestyles of eunuchs compared to non-castrated men may influence these findings. Eunuchs likely had a special, maybe even pampered, role in society. The other men likely were engaged in dangerous work. Recall that industrial and work-related accidents was one of the top 120 killers (in the USA) well into the 20th century.$\endgroup$
– Larry_ParnellSep 28 '12 at 20:33

The testosterone effect mentioned by @rwst is an exciting new discovery, but there may be a deeper answer which is an evolutionary adaptation. There is a theory called the grandmother effect that tries to guess why women live often quite a long time after menopause.

Longevity in women doesn't make a great deal of sense from the standpoint of selection, since a lifespan past popping out the little ones wouldn't really increase fecundity.

As you might guess, having a parent around for a long time after a human child is born might increase the number of offspring that reach the age. The grandmother effect surmises that females have a stronger, more direct relationship with offspring and can contribute directly to the viability of her offspring even after she stops having children herself. Grandfather's probably don't enjoy this benefit as much because they are thought to contribute less to the offspring. You have to remember that over the length of human history men's tendency has been to be a little more distant because of the difference in parental certainty. while it can be very low for fathers, it is pretty much zero for mothers.

It would be surprising if the grandmother effect were the only reason women live longer then men, but it sounds like a stronger selective effect to me and men can probably evolve longer lives by taking an interest in their offspring longer. This would have to be on an adaptive scale - over the entire population though.

Individual variations in longevity can of course be more important than these effects, but these theories try to explain the bias.